BACKGROUND: Pivampicillin is a prodrug which is widely used in Scandinavian countries for oral antibiotic therapy. The pivaloyl moiety has a carnitine depleting effect, which has caused doubts about the safety of administering pivampicillin during pregnancy. The aim of the study was to evaluate the risk of congenital malformations in general, preterm delivery and low birth weight in users of pivampicillin. METHODS: Seven hundred and ninety-one women who had redeemed a prescription of pivampicillin during their first pregnancy from 1 January 1991 to 31 December 1996 were identified in the North Jutland Pharmaco-Epidemiological Prescription Database. By linkage to the Danish Medical Birth Registry and Regional Hospital Discharge Registry we compared their birth outcomes (malformations, preterm delivery and low birth weight) with the outcomes in 7472 reference pregnancies on which the mother had not redeemed any prescription at all during pregnancy. RESULTS: The prevalence of malformations was 5.5% (11 cases) in offspring of 199 women who had used pivampicillin during the first trimester, and 5.6% (420 cases) in offspring of controls (OR: 0.95, 95% CI: 0.51-1.76). Furthermore, we did not find any significant risk of preterm delivery (OR: 0.75, 95% CI: 0.54-1.05) or low birth weight (OR: 0.93, 95% CI: 0.55-1.57). CONCLUSION: This study showed no increased risk of congenital malformations, preterm delivery or low birth weight in offspring of women who had redeemed a prescription for pivampicillin during pregnancy.